The present invention relates to a process and device for analyzing the movement of the eye or eyes of a patient, i.e. of a human being or animal.
The technical domain of the invention is that of the manufacture of devices for measuring the movement of the eyes.
The interest of the invention is, above all, medical. Its preferred application is the exploration of vertigos and disorders of balance, which are one of the principal pathologies with which doctors are faced (one patient out of twenty in general practice).
In this domain of preferred application of the invention, the eye is considered as an indicator of the activity of the vestibulum (or posterior labyrinth), which is an organ of balance located in the internal ear sensitive to the absolute position as well as to the movements of the head. This organ influences by reflex (therefore involuntarily) the tonus of all the skeletal muscles, in particular that of the eye muscles. When it is stimulated, either by movements of the head, or artificially, in particular by thermal effects in the internal ear, the vestibulum is capable of inducing automatic movements of the eyes or nystagmus, which are synchronous for the two eyes. Consequently, the observation of either one of these two eyes (if the eye muscles are normal) is an excellent reflection of the functioning of the vestibulum. However, account must be taken of a considerable constraint which results from the fact that the eye also responds to visual stimulations and that the system of vision takes priority and is more powerful than that of the vestibulum: observation of the nystagmus therefore indicates the functioning of the internal ear only if the patient is in total darkness, i.e. if his/her two eyes receive no visible light.
To test the vestibulum from the oculomotor indicator, several conditions must therefore be complied with:
the eye movements must be able to be permanently observed and/or analyzed during all the tests of the examination. PA1 the examination must be able to verify the normality of the voluntary eye movements and reflexes of visual origin, during so-called "tracking tests" which consist in projecting fixed or mobile targets or visual stimuli proposed for the patient's sight in the scene. PA1 the natural vestibular stimuli of displacement to which the patient is subjected and for which the oculomotor response is studied (essentially the movements of his head with respect to the scene or his head with respect to his thorax) must be able to be recorded and analyzed at the same time as the movements of the control eye. PA1 the examination must be able to include so-called "vestibular tests" during which the total absence of light visible solely by the patient is rendered necessary. PA1 in a window of the image centred on the mean position of the pupil and delivered by said first camera or eye observing camera, the contour of a shape corresponding to the pupil is isolated; PA1 if necessary, the contour of the pupil is rectified so as to render it substantially circular; PA1 the geometric centre of gravity of the contour, which is the position of the centre of the pupil, i.e. its two coordinates in a plane, is calculated; PA1 an angular portion of a ring located around the image of said pupil (comprising striae, in known manner) is compared or correlated with a previously recorded image of said angular ring, and an angle of rotation of said angular ring corresponding to an angle of rotation in said plane of said eye, is deduced. PA1 a window or a part of the scene image furnished by the second camera is used, said window being able, in a particular embodiment, to move in said image, PA1 the contours of different objects detected in said window are extracted, and the centres of gravity of the objects and/or of the corresponding contours are calculated, PA1 the contours thus detected which do not have a number of points included in an interval centred around the previously recorded number of points of a predetermined and sought after object, are eliminated, PA1 for each remaining contour, predetermined reduced contour shape functions are calculated, PA1 said reduced contour shape functions thus determined are compared with previously recorded contour shape functions corresponding to the sought-after object, PA1 the position in said window of said object thus identified is calculated and, in a particular embodiment, said window is recentred around said object.
In order better to understand the object of the present invention, account must also be taken of the fact that the constraint of tightness to visible light, although it is indispensable for the exploration of the vestibular activity, may become limitative in the case of more restrictive examinations made by other doctors, for whom the observation and analysis of the ocular movements presents a slightly different interest, when for example solely tracking tests or follow-up and analysis tests of the sight are made. In that case, a device according to the preferred application might be unsuitable if it does not provide in its embodiment that the solution made to the condition of tightness is carried out only as supplementary, secondary option, independent of the basic device.
The principal object of the present invention is therefore to provide a device and process for observation, measuring and analysis of eye movements, which makes it possible to implement during the same, preferably medical examination, the following four priorities, except the last for certain examinations, namely in order of priority, firstly, the necessity of being able to observe and/or analyze the movement of an eye at least during the whole of the examination; secondly, the necessity of being able to liberate the field of vision of an eye at least facing the scene; thirdly, the necessity of being able to observe and/or analyze, at the same time as the movements of at least one eye, all the visual and vestibular ocular stimuli, i.e. the movements of the visual targets with respect to the head, the movements of the head with respect to the scene and the movements of the head with respect to the thorax; fourthly, the necessity of being able totally to occult the two eyes from any visible light, i.e. of being able to place the patient in complete darkness during part of the examination.
Another object of the invention is to provide a device which is ergonomic, capable of being adapted to the morphology and/or sight of the patient, and of being economical, compact and light.
Patent Application EP 125 808 to WEINBLATT already discloses an eye movement measuring device which comprises a spectacle frame and which comprises, as shown in FIG. 2 of this document, a scene camera connected to optics fixed on a side piece of the spectacles by optical fibers, and which also comprises an eye observing camera connected to optics fixed on the spectacle frame, likewise via optical fibers; the video signals produced by the two cameras are combined to furnish an image corresponding to the superposition of the scene image with the image of the eye, which images are observed by the two cameras.
One object of the invention is to provide a device for measuring and analyzing the movement of the eyes comprising an eye observing camera and a camera for observing the scene in which the patient is placed, which device is improved with respect to the one described in the above document, whilst remaining compatible with the principal object. Other Patents or publications on eye movement measuring devices are also known, which comprise a scene camera in relation with an eye observing camera, in which the scene camera is placed and equipped so as to visualize, approximately or exactly, the field of vision of the observer. This latter object is not shared as far as the present invention is concerned, for which the sole function of the visualization of the scene is the observation and calculation of the relative movements of objects of the scene with respect to the patient's (observer's) head, and may consequently not correspond at all to the field of vision of the observer (as nothing prevents, in a particular configuration of the device, placing or projecting the objects of the device on the ceiling of the examination room and directing the scene camera upwardly), which has for its advantage to allow the present invention a freedom of configuration of the device in accordance with criteria which are adapted to the preferred examination and which bear on the positioning of the scene camera with respect to the ocular camera.